A figure used to historically set rail fares came in at 3.6% this year, ONS data showed on Wednesday.
July's retail price index reading had been used by the government until 2023 to determine train ticket price hikes.
Average wage growth and a figure of 4.9% have been used since to cap annual increases after inflation has soared in recent years.
Were the figure to be based on the retail price index once again, July’s reading has historically been used, with this sitting at 3.6% last month, according to data from the ONS.
A Department for Transport spokesperson commented: “No decisions have been made on next year’s rail fares but our aim is that prices are as affordable as possible for passengers.”
Westminster, alongside the Scottish and Welsh governments, regulates around 45% of fares on Britain’s railways, while others follow these closely due to contracts introduced during the pandemic.